In recent years, development has been promoted for wireless communication systems using RFID (Radio Frequency IDentification) technology for contactless tags. RFID systems perform wireless communication between a wireless transceiver called a reader/writer and an RFID tag.
RFID tags are expected to be utilized in various applications such as logistics management, merchandise management, shoplifting prevention, and the like, and have started being introduced in some of the applications, for example, merchandise tags and IC cards such as transportation cards. An RFID tag has an IC chip and an antenna for wireless communication with readers/writers. The antenna mounted in the tag receives carrier waves transmitted from readers/writers and thus operates a drive circuit in the IC chip.
RFID tags are expected to be used for every kind of merchandise. For that purpose, the production cost needs to be reduced, and studies have been made on flexible and inexpensive tags based on getting rid of production processes that use vacuum and high temperature and on using coating and printing technologies.
For example, for a drive circuit in an IC chip, using a field-effect transistor (hereinafter referred to as FET) has been proposed in which an organic semiconductor having excellent formability is used as a semiconductor layer. Utilizing an organic semiconductor as ink makes it possible to form a circuit pattern directly on a flexible substrate using inkjet technology, screening technology, and the like. In this regard, FETs in which carbon nanotubes (CNTs) or organic semiconductors are used in place of conventional inorganic semiconductors are vigorously studied (see, for example, Patent Document 1).
A drive circuit in an RFID tag generally includes a complementary circuit composed of a p-type FET and an n-type FET for purposes of suppression of power consumption and the like. It is known, however, that an FET using CNTs usually exhibits the characteristics of a p-type semiconductor device in the atmosphere. In addition, an FET using an organic semiconductor has a single channel. This does not enable a complementary circuit to be composed of the same materials, but different materials have to be selected for a p-type FET and an n-type FET, posing a problem in that the production processes are complicated, the production efficiency is decreased, and the production cost is increased.
For this reason, converting an FET using CNTs into an n-type semiconductor device by means of vacuum heating treatment or ion doping (see, for example, Patent Document 2 and Non-Patent Document 1) and using a bipolar organic semiconductor material (see, for example, Patent Documents 3 and 4) to form a complementary circuit from the same materials have been studied.